Categories

This study was conducted to evaluate the pure culture fermentation performance of eight strains of Brettanomyces with the objective to find characteristic compounds produced during fermentation. Colony formation and growth was initially observed on media agars recommended for use in the brewing industry with strong growth observed on MYPG, WLN, and CuSO4 agar medias. Cell growth during semi aerobic batch culture showed 2-phase and 3-phase growth patterns with maximum cell counts reached after 168 to 192 hours of propagation. Pure culture fermentations were conducted with multiple pitching rates and variation was observed in the different strains abilities to achieve adequate attenuation after 35 days. Longer time was needed for most strains except B. bruxellensis (BSI-Drie), which achieved 82.16% apparent attenuation with a pitching rate of 6×106 cells/ml. When the strains were pitched at a rate of 12×106 cells/ml a correlation was observed between final pH and final apparent attenuation, with a lower final pH resulting in greater attenuation. Fermentations were further conducted with wort pre-acidified with lactic acid at concentration of 100, 500, 1,000 and 3,000 mg/l. Higher initial concentrations of lactic acid had a significant effect, increasing the level of attenuation observed in each strain, while generally decreasing the secondary metabolites produced. Compound analysis of the fermented beers showed ethyl acetate, ethyl caproate, and ethyl caprylate were the significant esters produced with no isoamyl acetate detected throughout the study. Of the esters produced, ethyl caproate and ethyl caprylate were produced at levels previously unseen in fermented beer.